Rfid tag with integrated antenna

ABSTRACT

A radio frequency identification (RFID) tag. In one embodiment, an RFID tag includes an integrated circuit die. The integrated circuit die includes circuitry configured to store information and transmit the stored information responsive to reception of a radio frequency (RF) signal. The integrated circuit die also includes an antenna coupled to the circuitry. The antenna is configured to transmit and receive RFID signals. Further, the antenna and the interconnects of the circuitry are formed of a same metal, and fabricated using a same semiconductor process.

BACKGROUND

Radio frequency identification (RFID) tag technology has gained enormousattention due to its commercial application in various fields, includingintelligent transportation systems, commerce, and security. Using RFIDtechnology, an RFID tag is attached to an object to identify or track.The RFID tag communicates with an RFID reader via transmission andreception of radio signals to allow the reader to identify and/or trackthe object. With increasing advance of technologies in integratedcircuits (ICs), the size of the ICs, such as RFID tags, is shrinking tostrike a balance between optimal performance and cost of fabrication.

SUMMARY

Various radio frequency identification (RFID) tag systems are disclosedherein. In some embodiments, an RFID tag includes an integrated circuitdie. The integrated circuit die includes circuitry configured to storeinformation and transmit the stored information responsive to receptionof a radio frequency (RF) signal. The die also includes an antennacoupled to the circuitry. The antenna is configured to transmit andreceive RFID signals. Further, the antenna and the interconnects of thecircuitry are formed of a same metal, and fabricated using a samesemiconductor process.

In accordance with at least some embodiments, an RFID tag includes asubstrate, circuitry disposed on a first layer of the substrate and anantenna disposed on a second layer of the substrate. The circuitry isconfigured to send identification information of the RFID tag uponreception of a RF signal from a receiver. The antenna is coupled to thecircuitry and is configured to transmit and receive RFID signals. Eachof the antenna and the circuitry include at least one layer of aconductive material that is plated onto the substrate using a samefabrication process.

In accordance with yet other embodiments, a RFID antenna includes anantenna loop array configured to be disposed on a first side of anintegrated circuit die. The antenna loop array is formed of at least onelayer of aluminum that is at least four micrometers thick. The antennaloop array is configured to wirelessly communicate with an RFID tagreader via a band centered about 13 megahertz.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of exemplary embodiments of the invention,reference will now be made to the accompanying drawings in which:

FIG. 1 shows a block diagram of a radio frequency identification (RFID)system in accordance with various embodiments;

FIG. 2 shows a block diagram of a RFID tag with an integrated antenna inaccordance with various embodiments.

FIG. 3 illustrates a top view of a RFID tag die with an integratedantenna in accordance with various embodiments; and

FIG. 4 illustrates a cross-sectional view of a RFID tag die with anintegrated antenna in accordance with various embodiments.

NOTATION AND NOMENCLATURE

Certain terms are used throughout the following description and claimsto refer to particular system components. As one skilled in the art willappreciate, companies may refer to a component by different names. Thisdocument does not intend to distinguish between components that differin name but not function. In the following discussion and in the claims,the terms “including” and “comprising” are used in an open-endedfashion, and thus should be interpreted to mean “including, but notlimited to . . . .” Also, the term “couple” or “couples” is intended tomean either an indirect or direct electrical connection. Thus, if afirst device couples to a second device, that connection may be througha direct electrical connection, or through an indirect electricalconnection via other devices and connections. The term “approximately”indicates an allowable variance of ±10% from a stated value.Accordingly, approximately “10” includes a range or 9-11.

DETAILED DESCRIPTION

The following discussion is directed to various embodiments of theinvention. Although one or more of these embodiments may be preferred,the embodiments disclosed should not be interpreted, or otherwise used,as limiting the scope of the disclosure, including the claims. Inaddition, one skilled in the art will understand that the followingdescription has broad application, and the discussion of any embodimentis meant only to be exemplary of that embodiment, and not intended tointimate that the scope of the disclosure, including the claims, islimited to that embodiment.

A radio frequency identification (RFID) tag includes an antenna thatprovides an interface to the wireless medium for communication and powercapture. To provide the needed level of efficiency, some conventionalRFID tags include a discrete antenna coupled to the RFID integratedcircuit (IC). Other conventional RFID tags may include an integratedantenna, but to provide the requisite efficiency such an antenna mustconventionally be fabricated using a different process than is appliedto construct the active circuitry of the tag. Neither conventionalalternative is desirable due increased fabrication costs and/orincreased tag size. As IC size decreases, conventional approaches toRFID tag antenna construction serve as impediments to tagminiaturization.

Embodiments of the present disclosure include an RFID tag with anintegrated aluminum antenna. The RFID antenna is capable of efficientoperation in the 13 megahertz (MHz) frequency range. Further, thedisclosed RFID antenna occupies an area not larger than RFID tagcircuitry to which the RFID antenna is coupled, and the antenna and thecircuitry are constructed using the same fabrication(semiconductor/metallization) process. Thus, embodiments of the RFID tagdisclosed herein advantageously provide optimal performance whilereducing overall tag cost and size

FIG. 1 shows a block diagram of an RFID system 100 in accordance withvarious embodiments. The system 100 includes an RFID reader 104, anobject 106, and a RFID tag 102 attached to the object 106. The object106 may be any physical entity to which the RFID tag 102 can beattached. The RFID reader 104 is an interrogation device that retrievesinformation from RFID tags in the vicinity of the reader 104. The RFIDreader 104 exposes the RFID tag 102 to electromagnetic radiation (e.g.,wireless signal 101) that activates (e.g., powers) the RFID tag 102.Responsive to the radio frequency signal 101, the RFID tag 102 performsvarious operations. For example, the RFID tag 102 may transmit encodedinformation, via a wireless signal 103, to the RFID reader 104. As such,the reader 104 may function as an interrogator that retrievesinformation associated with the object 106 from the RFID tag 102.Alternatively or additionally, the reader 104 may be coupled to externalsystems (not shown) that provide data storage and analysis or trigger afurther action. Although as a matter of concision FIG. 1 shows only asingle reader 104, and RFID tag 102, in practice, the system 100 mayinclude any number of readers and/or RFID tags. The RFID tag 102includes a novel integrated antenna 108 that allows the cost of the RFIDtag 102 to be reduced without loss of performance.

FIG. 2 shows a block diagram of the RFID tag 102. The RFID tag 102includes tag circuitry 200 and the integrated antenna 108. The tagcircuitry 200 includes storage 202 and transceiver 204. The tagcircuitry 200 may include other components and subsystems that have beenomitted from FIG. 2 in the interest of clarity. For example, thecircuitry 200 may include a power subsystem, a processor, etc. Thestorage 202 may include non-volatile memory such as FLASH memory,read-only memory (ROM), electrically-erasable programmable ROM, etc. Thestorage 202 may also include volatile memory, such as static randomaccess memory. The storage 202 may store identification information ofthe RFID tag 102 that is to be wirelessly transmitted to the reader 104.

The transceiver 204 is coupled to the antenna 108. The transceiver 204receives electrical signals generated by the antenna 108 responsive toRF signals transmitted by the reader 104, and transmits, via the antenna108, information, such as the identification information stored instorage 202. The transceiver 204 may initiate transmission responsive toreception of a radio frequency signal (e.g., signal 101) transmitted bythe reader 104.

To operate the RFID tag 102, the RFID tag 102 utilizes a voltage inducedby the inductance of the antenna 108 in the RFID tag 102, based onAmpere's law and Faraday's law, which state that flowing current in aconductor (e.g., an antenna loop) produces a magnetic field around theconductor; and a time-varying magnetic field through a surface boundedby a closed path induces a voltage around the loop. More particularly, aresonant frequency, f, of the antenna 108 is determined as:

${f = \frac{1}{2\pi \sqrt{LC}}},$

where:L is the inductance of the antenna 108; andC is the capacitance of the antenna 108 including parasitic capacitor.Thus, in order to effectively utilize the RFID tag 102 at a desiredoperating frequency, parameters of the antenna 108, including L and C,must be finely tuned.

Embodiments of the RFID tag 102 may communicate with the reader 104using a wireless frequency band centered at 13 MHz. Accordingly, in suchembodiments, the antenna 108 is tuned to operate in the 13 MHz band. Inconventional RFID tags, an antenna suitable for operation in the 13 MHzband increases the size and/or cost of the tag because additionalprocess steps and/or real estate are required. The antenna 108advantageously requires no more real estate than the active circuitry200 of the tag 102 and can be fabricated using the samesemiconductor/metallization process as the active circuitry 200.Accordingly, embodiments of the antenna 108 allow the size and cost ofthe RFID tag 102 to be reduced relative to conventional antennaimplementations.

FIG. 3 illustrates a top view of a RFID tag die 300, including views ofmultiple layers, with an integrated antenna 108 for use in the RFID tag102 in accordance with various embodiments. The die 300 integrates allthe components of the tag 102. The die 300 includes antenna loops 302, aplurality of interconnects 304, a plurality of antenna pads 306 and tagcircuitry 200 (not shown in FIG. 2). The tag circuitry 200 is disposedon a different layer of the die 300 from the antenna loops 302. In anembodiment, the antenna loops 302 comprise a plurality of rectangularelectrode patterns which may be referred to as an antenna loop array.Although the patterns shown herein are rectangular in shape, in someembodiments, the patterns of the antenna loops 302 may be rectangular,circular, multi-sided, or combinations thereof.

Still referring to FIG. 3, the circuitry 200 is coupled to the antennapads 306. The circuitry 200 electrically communicates with the antennaloops 302 via the interconnects 304 and the antenna pads 306. In someembodiments, the circuitry 200 may be an application-specifiedintegrated circuit (ASIC) or other type of integrated circuit. Theantenna loop 302 is configured to receive (e.g., 101 in FIG. 1) andtransmit (e.g., 103 in FIG. 1) RFID signals and, based on the receivedsignal 101, to induce a supplied voltage to power the circuitry 200 viathe interconnects 304 and the antenna pads 306. The circuitry 200 drivesthe information stored in the RFID tag die 300 to the antenna loops 302.In some preferred embodiments, the antenna pads 306 may serve as testpads, used to connect with external antennas for testing.

In some embodiments, the metal interconnects formed with regard to theactive circuitry 200 of the tag 102, the antenna loops 302, theinterconnects 304 and the antenna pads 306 are all formed of aluminum,and are deposited on the die 300 using a same semiconductor process,thereby reducing fabrication cost. The semiconductor process may includeelectron beam vapor deposition, molecular beam epitaxy, or sputtering.In some embodiments, the area of the antenna loops 302 is constrained tobe no more than the area of the active tag circuitry 200. Consequently,integrating the antenna 108 does not increase the size of the die 300.The antenna loops 302 may have an inductance of approximately 5microhenries (μH). The antenna loops 302 may include approximately 80loops, or turns, within the area of the RFID tag die 300. In someembodiments, the antenna loops 302 may have an inductance of at least 5μH or an inductance of at least 3 μH, and include at least 50 turns orat least 80 turns. In some embodiments, the total area of the die 300may be approximately one square millimeter in area. In other embodimentsthe area of the die 300 may be no more than one square millimeter (mm).

FIG. 4 illustrates a cross-sectional view of the RFID tag die 300 withintegrated antennas 302 in accordance with various embodiments. FIG. 4is a view of cross-section “A-A” of the antenna loops 302 depicted inFIG. 3. Section A-A shows a plurality of aluminum segments 404, spacedwith gaps 406, of antenna loops 302. The antenna loops 302 are disposedon silicon die 402, which includes the circuitry 200 electricallycoupled to the antenna loops 302. Each segment 404 of antenna loops 302may have a width of approximately 1.5 micrometers (μm). The thickness ofthe aluminum of the antenna loops 302 may greater than that applied tostandard interconnects. In some embodiments, the antenna loops may havea thickness of at least approximately 4 μm (i.e., 3.6 μm or more). Theantenna loops may include a spacing gap 406 approximately 2 μm in width.Although the cross section of each antenna loop 302 shown in FIG. 4 isillustrated as having a rectangular shape, the cross sectional geometrymay include geometries of other shapes such as a semi-circle, trapezoid,square, polygon, circle, triangle, or combinations thereof.

The above discussion is meant to be illustrative of the principles andvarious embodiments of the present invention. Numerous variations andmodifications will become apparent to those skilled in the art once theabove disclosure is fully appreciated. It is intended that the followingclaims be interpreted to embrace all such variations and modifications.

What is claimed is:
 1. A radio frequency identification (RFID) tag,comprising: an integrated circuit die, comprising: circuitry configuredto: store information; and transmit the stored information responsive toreception of a radio frequency signal; and an antenna coupled to thecircuitry, and configured to transmit and receive RFID signals; whereinthe antenna and interconnects of the circuitry are formed of a samemetal, and are fabricated using a same semiconductor process.
 2. TheRFID tag of claim 1, wherein the circuitry is disposed on a first layerof the die and the antenna is disposed on a second layer of the die; andwherein the antenna occupies an area of the second layer no larger thanan area of the first layer occupied by the circuitry.
 3. The RFID tag ofclaim 1, wherein the metal is aluminum.
 4. The RFID tag of claim 3,wherein the aluminum of the antenna is approximately 4 micrometers ormore in thickness.
 5. The RFID tag of claim 2, wherein the antennacomprises at least 50 loops.
 6. The RFID tag of claim 1, wherein theantenna has an inductance of at least 3 microhenries.
 7. The RFID tag ofclaim 1, wherein the antenna is tuned to operate in an RF range centeredabout 13 megahertz.
 8. The tag of claim 1, wherein the die isapproximately one square millimeter or less in area.
 9. The RFID tag ofclaim 1, wherein the RFID tag is attached to an item, and is configuredto provide tracking of the item based on RF signals transmitted via theantenna.
 10. A radio frequency identification (RFID) tag, comprising: asubstrate; circuitry disposed on a first layer of the substrate, thecircuitry configured to send identification information of the RFID tagupon reception of a radio frequency signal from a reader; and an antennacoupled to the circuitry, wherein the antenna is disposed on a secondlayer of the substrate and is configured to transmit and receive RFIDsignals; wherein each of the antenna and the circuitry comprise at leastone layer of a conductive material that is plated onto the substrateusing a same fabrication process.
 11. The RFID tag of claim 10, whereinthe antenna occupies an area of the second layer no greater than an areaof the first layer occupied by the circuitry.
 12. The RFID tag of claim10, wherein the conductive material is aluminum.
 13. The RFID tag ofclaim 12, wherein the aluminum of the antenna is at least approximately4 micrometers thick.
 14. The RFID tag of claim 10, wherein the antennacomprises at least 50 loops.
 15. The RFID tag of claim 10, wherein theantenna has an inductance of at least 3 microhenries.
 16. The RFID tagof claim 10, wherein the antenna is tuned to operate in an RF rangecentered about 13 megahertz.
 17. The RFID tag of claim 10, wherein theRFID tag is attached to an item, and is configured to provide trackingof the item based on RF signals transmitted via the antenna.
 18. A radiofrequency identification (RFID) antenna, comprising: an antenna looparray configured to be disposed on a first side of an integrated circuitdie, wherein the antenna loop array is formed of at least one layer ofaluminum that is at least approximately 4 micrometers thick; wherein theantenna loop array is configured to wirelessly communicate with a RFIDtag reader via a band centered about 13 megahertz.
 19. The RFID antennaof claim 18, wherein the antenna loop array has an inductance of atleast 3 microhenries.
 20. The RFID antenna of claim 18, wherein eachloop of the antenna loop array is rectangular, circular, multi-sided, orcombinations thereof.